a) Field of the Invention
The present invention relates to a dynamic pressure bearing apparatus in which air dynamic pressure is generated in a radial bearing and a thrust bearing to support a shaft both in the radial and thrust directions. The present invention also relates to a data disk drive apparatus which employs the dynamic bearing apparatus.
b) Description of the Related Art
Recently, in the area of drive apparatus such as motors, various types of dynamic pressure bearing apparatus have been studied and proposed. In a dynamic pressure bearing apparatus of conventional technology, a radial bearing comprises a rotor, which is rotatably meshed with a fixed shaft, for example, and radial dynamic pressure generating grooves, which are formed on the circumference of said fixed shaft. Also, thrust bearings are constructed by an edge of the fixed shaft and the surface of the rotor which faces in the axial direction. The rotor is rotatably supported by the air dynamic pressure which is generated in the radial bearing and the thrust bearing.
The bearing apparatus using the air, however, has a viscosity of one thousandth compared to the bearing dynamic pressure using oil. As a result, the bearing apparatus of conventional technology are generally big and therefore likely to increase the size of the entire apparatus. They can provide excellent air dynamic pressure only at a high speed. Specifically, they are poor in the shaft support properly in the thrust direction and in controlling vibrations. For this reason, a compact hard disk drive (HDD) system has been demanded for many years. It is commonly believed that a low speed bearing apparatus cannot employ the air dynamic pressure. In addition, an air dynamic pressure bearing apparatus can catch more or less dust particularly when the bearing apparatus abrades when it starts moving or stops. The dust can be harmful to the apparatus such as a hard disk drive (HDD) system and the like in which cleanliness is critical.
Nonetheless, in the air dynamic pressure apparatus, a rotor is rotated in air creating an insulated state. If the air dynamic pressure bearing apparatus is used, for example, in a hard disk drive (HDD) system, static electricity generated on a data disk is likely to be accumulated on the rotor side. The accumulated static electricity may damage the MR (magnetic resister) type head.